require "test/unit"
class AboutBlocks < Test::Unit::TestCase
  def method_with_block
    result = yield
    result
  end

  def test_methods_can_take_blocks
    yielded_result = method_with_block {1 + 2}
    assert_equal 3,   yielded_result
  end

  def test_blocks_can_be_definded_with_do_end_too
    yielded_result = method_with_block do 1 + 2 end
    assert_equal 3,   yielded_result
  end
  
  def method_with_block_arguments
    yield("Jim")
  end
   
  def test_blocks_can_take_arguments
    result = method_with_block_arguments do |argument|
      assert_equal "Jim", argument
    end
  end

  def many_yields
    yield(:peanut)
    yield(:butter)
    yield(:and)
    yield(:jelly)
  end

  def test_methods_can_call_yield_many_times
    result = []
    many_yields {|item| result << item}
    assert_equal [:peanut, :butter, :and, :jelly], result
  end 

  def yield_tester
    if block_given?
      yield
    else
      :no_block
    end
  end

  def test_methods_can_see_if_they_have_been_called_with_a_block
    assert_equal :with_block,  yield_tester{:with_block}
    assert_equal :no_block,    yield_tester
  end

  def test_block_can_affect_variables_in_the_code_where_they_are_created
    value = :initlial_value
    method_with_block { value = :modified_in_a_block}
    assert_equal :modified_in_a_block, value
  end

  def test_blocks_can_be_assigned_to_variables_and_called_explicitly
    add_one = lambda {|n| n + 1}
    assert_equal 11,    add_one.call(10)
    assert_equal 11,    add_one[10]
  end

  def test_stand_alone_blocks_can_be_passed_to_methods_expecting_blocks
    make_upper = lambda {|n| n.upcase}
    result = method_with_block_arguments(&make_upper)
    assert_equal "JIM", result
  end

  def method_with_explicit_block(&block)
    block.call(10)
  end

  def test_methods_can_take_an_explicit_block_argument
    assert_equal 20, method_with_explicit_block{|n| n * 2}
    add_one = lambda{|n| n + 1}
    assert_equal 11, method_with_explicit_block(&add_one)
  end
end
